The invention relates to the recognition of pulse-like useful signals which are superimposed by noise signals. A preferred field of application of the invention is the recognition of signals reflected by a target such as the receiver signals in radar and sonar systems. The invention, in particular, relates to the exact recognition of the arrival time of such pulse-like signals if they are superimposed by noise. For the determination of the distance and the spatial position of a target, it is important to exactly determine the point of time when the echo pulse arrives at the receiver. This receiver might be an electroacoustic transducer of a sonar apparatus or might be the antenna of a radar system. Those received pulses are different in shape and duration from the pulses radiated to the target by the radar or sonar transmitter. A correct determination of the beginning of a sonar signal is also required for determining the position of a target by means of two or more hydrophones located spaced apart. This information of the arrival time of the signal normally is derived from the rising leading edge of the received sonar signal. If, however, this signal is superimposed by noise, the detection of the leading edge may result in an uncertain determination of the exact arrival time. In many cases the energy content of noise signals is in the same order as the energy content of the useful signal. In those cases it is not possible to distinguish useful signals from noise signals just by their amplitude.
It is an object of the invention to recognize pulse-like useful signals also in the case when those useful signals are superimposed by noise signals having a higher amplitude as the useful signals. In addition to the distinction between useful signals and noise signals, the invention further relates to the determination of the beginning and the duration of such useful signals which are superimposed by noise signals.